STEGANOGRAPHY

STEGANOGRAPHY - the practice of hiding an image, message, audio or video file within another.
Early examples included tattooing messages onto the shaved heads of couriers and waiting for their hair to grow before despatching them, using a child to send messages using different seed types to denote how many of each weapon the enemy had and hiding messages within commercial orders. More recently, digital techniques have been possible, such as 'chaffing and winnowing' - first mixing information with harmless random data and then discarding the random data at the other end to reveal the original message. Other techniques include using freely-available software and making the text the same colour as the background on documents, as in this example; I have written this in white on a white background.All you have to do is change the text colour to make this visible.

 BELOW: STEGANOGRAPHY USING DIGITAL IMAGES